The present invention relates to a fuel injection system for injecting fuel into a combustion chamber of an internal combustion engine and, more particularly, to a fuel injection system especially suitable for a diesel engine.
Conventionally, a fuel injection system is provided in a diesel engine so as to inject fuel into a combustion chamber of the engine. In general, a fuel injection system of this type comprises a combination of a fuel delivering means such as a fuel injection pump and a nozzle unit for pressurizing the fuel so as to inject the fuel into the combustion chamber. In this system, the fuel delivered from the fuel delivering means is fed to the nozzle unit and is injected from a nozzle of the nozzle unit into the combustion chamber.
In this type of fuel injection system, the amount of fuel to be injected into the combustion chamber must vary in accordance with the operating conditions of the engine. For example, when the driver strongly depresses the accelerator pedal or the engine is operated at a high load, the amount of fuel to be injected must be increased. However, when the engine is operated at a low load, the amount of fuel to be injected must be decreased.
For this reason, in the fuel injection system, the fuel delivering means has the function of adjusting the amount of injected fuel in accordance with the operating conditions of the engine. Therefore, a proper amount of fuel must be delivered from the fuel delivering means to the nozzle unit. The fuel is then injected from the nozzle unit to the combustion chamber.
A check valve is also disposed to prevent reverse flow of the fuel toward the fuel delivering means when the fuel supplied from the fuel delivering means is pressurized and injected. This check valve allows proper high-pressure injection of the fuel and highly precise adjustment of an injection amount corresponding to the operating conditions of the engine.
However, when the check valve described above is used, the pressurization efficiency of the fuel is often degraded to an extent corresponding to the volume of the check valve. If leakage occurs in the check valve, the pressurization efficiency is degraded and at the same time the injection amount cannot be properly delivered. Furthermore, use of the check valve results in an increase in the number of component parts of the nozzle unit and hence a large size unit.